Change error log to warning for removing multicast vif

Removing a multicast virtual interface with setsockoptMrt6DelMif may
return error if the interface is already gone. This is expected behavior
and should be logged as a warning instead of error.

Bug: 400596719
Change-Id: I11bfe22be5dc2479768dbc1b53eb7feeec27af3f
1 file changed